ESD protection circuit

ABSTRACT

One embodiment of the disclosure provides an electrostatic discharge protection circuit. The electrostatic discharge protection circuit includes a p-type field effect transistor, a capacitance device and an n-type field effect transistor. The p-type field effect transistor has a source coupled to an input/output terminal, a gate coupled to a first node and a drain coupled to a second node. The capacitance device has a first terminal coupled to a first rail and a second terminal coupled to the first node. The n-type field effect transistor has a source coupled to the first rail, a gate coupled to the second node and a drain coupled to the first node.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of application Ser. No. 13/149,176, filed on May 31, 2011, which claims priority of Taiwan Patent Application No. 099146287, filed on Dec. 28, 2010, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electrostatic discharge (ESD) protection circuit, and in particular relates to an electrostatic discharge (ESD) protection circuit with low leakage, high trigger speed and parasitic silicon controlled rectifier (SCR).

2. Description of the Related Art

FIG. 1 shows a conventional electrostatic discharge protection circuit 100. The conventional protection circuit 100 has an electrostatic discharge detecting circuit 110, and the electrostatic discharge detecting circuit 110 has a trigger node 106. The trigger node 106 of the electrostatic discharge detecting circuit 110 is coupled to a silicon controlled rectifier 112. When an event of the electrostatic discharge occurs, the trigger node 106 produces a trigger current to trigger the silicon controlled rectifier 112. After the silicon controlled rectifier 112 is triggered by the trigger current, the silicon controlled rectifier 112 provides a discharge path to discharge the electrostatic discharge current from the rail V_(DD) to the rail V_(SS).

With the progress in process techniques, new process techniques are able to reduce the size of metal-oxide-semiconductor field effect transistor (MOSFET) into a nanometer order. Thus, the leakage current of the gate oxide of metal-oxide-semiconductor field effect transistor (MOSFET) is increased, because the thickness of the gate oxide is reduced. The on-chip electrostatic discharge protection circuit, particularly the MOS capacitor, usually adopts a large size metal-oxide-semiconductor field effect transistor (MOSFET) when designing the circuit. Therefore, the electrostatic discharge protection circuit suffers from leakage current and inefficient system power usage in normal operating mode. To solve the leakage current of MOSFETs, most of the conventional electrostatic discharge protection circuits use a thick oxide device with high mask costs and low protection ability against electrostatic discharge, such that the electrostatic protection circuits require more space to improve the protection ability. Therefore, a low leakage electrostatic protection circuit is in need.

BRIEF SUMMARY OF THE INVENTION

A detailed description is given in the following embodiments with reference to the accompanying drawings.

One embodiment of the disclosure provides an electrostatic discharge protection circuit. The electrostatic discharge protection circuit includes a p-type field effect transistor, a capacitance device and an n-type field effect transistor. The p-type field effect transistor has a source coupled to an input/output terminal, a gate coupled to a first node and a drain coupled to a second node. The capacitance device has a first terminal coupled to a first rail and a second terminal coupled to the first node. The n-type field effect transistor has a source coupled to the first rail, a gate coupled to the second node and a drain coupled to the first node.

Another embodiment of the disclosure provides an electrostatic discharge protection circuit. The electrostatic discharge protection circuit includes a p-type field effect transistor, a capacitance device and an n-type field effect transistor. The p-type field effect transistor has a source coupled to a first rail, a gate coupled to a first node and a drain coupled to a second node. The capacitance device has a first terminal coupled to a second rail and a second terminal coupled to the first node. The n-type field effect transistor has a source coupled to an input/output terminal, a gate coupled to the second node and a drain coupled to the first node.

Another embodiment of the disclosure provides an electrostatic discharge protection circuit. The electrostatic discharge protection circuit includes a p-type field effect transistor, a capacitance device and an n-type field effect transistor. The p-type field effect transistor has a source coupled to a first rail, a gate coupled to a first node and a drain coupled to a second node. The capacitance device has a first terminal coupled to a second rail and a second terminal coupled to the first node. The n-type field effect transistor has a source coupled to the second rail, a gate coupled to the second node and a drain coupled to the first node.

One embodiment of the disclosure further provides an electrostatic discharge protection circuit. The electrostatic discharge protection circuit includes a substrate, a first N-well, a second n-type doped region, a third n-type doped region, a p-type field effect transistor, an n-type field effect transistor, and a capacitance device. The substrate has a first contact point, a second contact point and a first n-type doped region. The first N-well is formed in the substrate, having a third contact point coupled to a first rail. The second n-type doped region is formed on the first N-well and coupled to the first rail. The third n-type doped region is formed on the first N-well and coupled to a first node. The p-type field effect transistor is formed on the first N-well, wherein the p-type field effect transistor further includes a first p-type doped region, a first gate and a second p-type doped region. The first p-type doped region is formed on the first N-well and coupled to a second node. The first gate is coupled to the first node. The second p-type doped region is formed on the first N-well and coupled to the first rail. The n-type field effect transistor is formed on the substrate, wherein the n-type field effect transistor further includes a second gate, a fourth n-type doped region and a fifth n-type doped region. The second gate is coupled to the second node. The fourth n-type doped region is formed on the substrate and coupled to a second rail. The fifth n-type doped region is formed on the substrate and coupled to the first node. The capacitance device has a first terminal coupled to the second rail and a second terminal coupled to the first node, wherein the second contact point is coupled to the second node, and the first contact point and the first n-type doped region are coupled to the second rail.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a schematic view of a conventional electrostatic discharge protection circuit.

FIG. 2A is a schematic view showing an embodiment of the electrostatic discharge protection circuit.

FIG. 2B is a layout of the electrostatic discharge protection circuit shown in FIG. 2A.

FIG. 2C is another layout of the electrostatic discharge protection circuit shown in FIG. 2A.

FIGS. 2D-2V are a plurality of schematic views showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A.

FIG. 3A is a schematic view showing another embodiment of the electrostatic discharge protection circuit.

FIG. 3B is a layout of the electrostatic discharge protection circuit shown in FIG. 3A.

FIG. 3C is another layout of the electrostatic discharge protection circuit shown in FIG. 3A.

FIG. 3D is another layout of the electrostatic discharge protection circuit shown in FIG. 3A.

FIGS. 3E-3I are a plurality of schematic views showing another embodiment of the electrostatic discharge protection circuit of FIG. 3A.

FIG. 4A is a schematic view showing another embodiment of the electrostatic discharge protection circuit.

FIG. 4B is a layout of the electrostatic discharge protection circuit shown in FIG. 4A.

FIG. 4C is another layout of the electrostatic discharge protection circuit shown in FIG. 4A.

FIGS. 4D-4H are a plurality of schematic views showing another embodiment of the electrostatic discharge protection circuit of FIG. 4A.

FIG. 5A is a simulation diagram of leakage current in the disclosure.

FIG. 5B is a simulation diagram of leakage current in the conventional electrostatic discharge protection circuit.

FIG. 6A is a simulation diagram of trigger current in the disclosure.

FIG. 6B is a simulation diagram of trigger current in the conventional electrostatic discharge protection circuit.

FIG. 7A is a schematic view showing another embodiment of the electrostatic discharge protection circuit.

FIGS. 7B-7F are a plurality of schematic views showing another embodiment of the electrostatic discharge protection circuit of FIG. 7A.

FIG. 7G is a layout of the electrostatic discharge protection circuit shown in FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carrying out the disclosure. This description is made for the purpose of illustrating the general principles of the disclosure and should not be taken in a limiting sense. The scope of the disclosure is best determined by reference to the appended claims.

FIG. 2A is a schematic view showing an embodiment of the electrostatic discharge protection circuit. As shown in FIG. 2A, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210 and an n-type field effect transistor 212. The first resistor 202 has a first terminal coupled to the rail V_(DD) and a second terminal coupled to the first node N1. The p-type field effect transistor 204 has a source coupled to the rail V_(DD), a gate coupled to the first node N1 and a drain coupled to the first diode 210. The first diode 210 has an anode coupled to the drain of the p-type field effect transistor 204 and a cathode coupled to the second node N2. The second diode 206 has an anode coupled to the first node N1 and a cathode coupled to the n-type field effect transistor 212. The diode device 208 has a first terminal coupled to the rail V_(SS) and a second terminal coupled to the first node N1. The n-type field effect transistor 212 has a source coupled to the rail V_(SS), a gate coupled to the second node N2 and a drain coupled to the cathode of the second diode 206. The trigger current I-trigger1 is inputted to a parasitic silicon controlled rectifier or a discharge device from the node N2.

It should be noted that, in the embodiment, diode device 208 serves as a capacitance device and is applied to construct an RC circuit with the first resistor 202. In some embodiment, the diode device 208 has a first terminal coupled to the second node N2 and a second terminal coupled to the first node N1, and the diode device 208 can be replaced by the other capacitance components depending on the need of applications as appropriate, such as plate capacitors, MOS capacitors or the same. Compared with the other capacitance components, the diode device 208 can reduce the area of the electrostatic discharge protection circuit 200. In addition, the electrostatic discharge protection circuit 200 further comprises a parasitic silicon controlled rectifier 214 which comprises the p-type field effect transistor 204 and the n-type field effect transistor 212. The parasitic silicon controlled rectifier 214 has a control terminal coupled to the second node N2, and the control terminal can trigger the parasitic silicon controlled rectifier 214 by the trigger current I-trigger1. When an electrostatic discharge event occurs, the parasitic silicon controlled rectifier 214 provides a discharge path to protect the chip. In another embodiment, the electrostatic discharge protection circuit 200 can further be coupled to the discharge device 290 (ex. clamp device or other silicon controlled rectifier device) between the rail V_(DD) and V_(SS). In the electrostatic discharge event, the discharge device 290 can be triggered by the electrostatic discharge protection circuit 200 from the second node N2 and provides a discharge path for the chip. Note that, the electrostatic discharge protection circuit 200 can be regarded as a detecting circuit after being coupled to the discharge device 290.

FIG. 2B is the layout of the electrostatic discharge protection circuit 200. As shown in FIG. 2B, the electrostatic discharge protection circuit 200 includes a substrate 216, a first resistor 202, a first diode 210 and a second diode 206. The diode device 208 can be replaced by the other capacitance components, such as plate capacitors, MOS capacitors or the same. The substrate 216 includes an N-well 218, at least one N-well 220, a diode device 208, a p-type field effect transistor 204 and an n-type field effect transistor 212. It should be noted that the n-type and the p-type doped regions can be served as a plurality of contact points. For example, in this embodiment, the p-type doped region 252 can be served as a first contact point, the n-type doped region 248 can be served as a second contact point, the n-type doped region 246 can be served as a third contact point, and the p-type doped region 250 can be served as a fourth contact point.

The substrate 216 further has the first contact point (that is, the p-type doped region 252) and the fourth contact point (that is, the p-type doped region 250). The first and fourth contact points are coupled to the rail V_(SS) and the cathode of the first diode 210, respectively. The first resistor 202 has a first terminal coupled to the rail V_(DD) and a second terminal coupled to the anode of the second diode 206. The N-well 218 is formed on the substrate 216 and has the second contact point (that is, n-type doped region 248) coupled to the rail V_(DD). The N-well 220 is formed on the substrate 216 and has the third contact point (that is, n-type doped region 246) coupled to the second terminal of the first resistor 202. The diode device 208 is a capacitance diode constructed via the N-well 220 and the substrate 216. It should be noted that the substrate 216 can be a p-type semiconductor substrate or a p-type semiconductor substrate having a P-well, wherein the n-type field effect transistor 212 is formed in the P-well. In another embodiment, the diode device 208 can be a common capacitor device and coupled between the second terminal of the first resistor 202 and the rail V_(SS).

The p-type field effect transistor 204 is formed on the N-well 218, comprising the p-type doped region 222, the first gate 224 and the p-type doped region 226. The p-type doped region 222 is the drain of the p-type field effect transistor 204 and is formed in the N-well 218 and coupled to the anode of the first diode 210. The first gate 224 is the gate of the p-type field effect transistor 204, and coupled to the second terminal of the first resistor 202 (that is the first node N1). The p-type doped region 226 is the source of a p-type field effect transistor 204 and is formed in the N-well 218 and coupled to the rail V_(DD).

The n-type field effect transistor 212 is formed on the substrate 216, comprising the second gate 228, the n-type doped region 230 and the n-type doped region 232. The second gate 228 is coupled to the cathode of the first diode 210. The n-type doped region 230 is the source of the n-type field effect transistor 212 and is formed on the substrate 216 and coupled to the rail V_(SS). The n-type doped region 232 is the drain of the n-type field effect transistor 212 and is formed on the substrate 216 and coupled to the cathode of the second diode 206.

The substrate 216 further includes the parasitic silicon controlled rectifier 214, the n-type doped regions 246-248, the p-type doped regions 250-252 and the shallow trench isolations 254-264. In this embodiment, the p-type doped region 226 of the p-type field effect transistor 204, the N-well 218, the substrate 216 and the n-type doped region 230 of the n-type field effect transistor 212 form a parasitic silicon controlled rectifier 214 in the substrate 216. Moreover, the fourth contact point (that is, p-type doped region 250), which is coupled to the cathode of the first diode 210, is arranged to be a control terminal of the parasitic silicon controlled rectifier 214. The n-type doped regions 246 and 248 serve as the third contact point (that is, n-type doped region 246) and the second contact (that is, the n-type doped region 248), respectively. The p-type doped regions 250 and 252 serves as the fourth contact point (that is, the p-type doped region 250) and the first contact point (that is, the p-type doped region 252), respectively. The shallow trench isolation 254-264 is disposed between the doped regions to isolate the doped regions. For instance, the shallow trench isolation 254 is arranged to isolate the n-type doped region 246 of the N-well 220 and the n-type doped region 248 of the N-well 218. The shallow trench isolation 256 is arranged to isolate the n-type region 248 and the p-type doped region 222 of the p-type field effect transistor 204. The shallow trench isolation 258 is arranged to isolate the p-type doped region 226 of the p-type field effect transistor 204 and the p-type doped region 250 of the substrate 216. The shallow trench isolation 260 is arranged to isolate the n-type doped region 230 of the n-type field effect transistor 212 and the p-type doped region 250 of the substrate 216. The shallow trench isolation 262 is arranged to isolate the n-type doped region 232 of the n-type field effect transistor 212 and the p-type doped region 252 of the substrate 216. The shallow trench isolation 264 is arranged to isolate the p-type doped region 252 of the substrate 216 and the n-type doped region 246 of the second N-well 220. Furthermore, the N-well 218 of the electrostatic discharge protection circuit 200 can also be laterally extended to be under the fourth contact point (that is, under the p-type doped region 250), as FIG. 2C shows.

When an electrostatic discharge event occurs, the electrostatic discharge protection circuit 200 of FIGS. 2A and 2B discharges the electrostatic current from the rail V_(DD) to the rail V_(SS) to protect the chip. At this time, the voltage level at the gate of the p-type field effect transistor 204 (i.e., the first gate 224) is lower than that at the rail V_(DD) because of the RC delay formed by the first resistor 202 and diode device 208. Therefore, the p-type field effect transistor 204 is conducted by the voltage difference between the source and gate thereof.

The conducted p-type field effect transistor 204 turns on the first diode 210 to produce the trigger current I-trigger1, which is output to the fourth contact point (that is, the p-type doped region 250) to trigger the parasitic silicon controlled rectifier 214. After the parasitic silicon controlled rectifier 214 is triggered, the parasitic silicon controlled rectifier 214 discharges the electrostatic current from the rail V_(DD) to the rail V_(SS). In the meantime, the voltage of the second node N2 is increased because the p-type field effect transistor 204 and the first diode 210 are turned on, and the n-type field effect transistor 212 is turned on by the voltage difference of the source (that is, the n-type doped region 230) and the gate (that is, the second gate 228). The conducted n-type field effect transistor 212 turns on the second diode 206. Since the second diode 206 is turned on, the voltage of the first node N1 is decreased, such that the current on the conducted p-type field effect transistor 204 is increased. In light of the foregoing, the p-type field effect transistor 204 and n-type field effect transistor 212 constitute a loop, such that the p-type field effect transistor 204 and n-type field effect transistor 212 are fully conducted (i.e., turned on) and provide the trigger current to the silicon controlled rectifier 214 continuously. Furthermore, as the FIG. 2B shows, the fourth contact point (that is, the p-type doped region 250) and the first contact point (that is, the p-type doped region 252) forms a parasitic resistor 266 in the substrate 216.

In another embodiment, the electrostatic discharge protection circuit 200 of FIGS. 2A and 2B further comprises a first diode string 272 and a second diode string 274 as FIG. 2D shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. As described above, the second diode string 274 is coupled with the second diode 206 in series. The voltage difference between the gate (that is, the second gate 228) and the drain (that is, the n-type doped region 232) of the n-type fled effect transistor 212 can be decreased by tuning the diode number of the second diode string 274 to reduce the leakage of the n-type field effect transistor 212. In a similar way, the first diode string 272 and the first diode 210 are coupled in series, and the leakage of the p-type field effect transistor 204 can be reduced as the voltage difference between the gate (that is, the first gate 224) and the drain (that is, the p-type doped region 222) of the p-type field effect transistor 204 is reduced by tuning the diode number of the first diode string 272.

FIG. 2E is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2E, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210 and an n-type field effect transistor 212. FIG. 2E is similar to FIG. 2A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2E further comprises a first diode string 272 and a second diode string 274 as FIG. 2F shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272 and the second diode string 274. In yet another embodiment, the p-type field effect transistor 204 of the electrostatic discharge protection circuit 200 of FIG. 2E further has a buck terminal coupled to the rail V_(DD) as FIG. 2G shows. Therefore, a parasitic diode 205 is formed between the input/output terminal 280 and the rail V_(DD) when the buck terminal of the p-type field effect transistor 204 is coupled to the rail V_(DD).

FIG. 2H is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2H, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208 and an n-type field effect transistor 212. FIG. 2H is similar to FIG. 2A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2H further comprises a second diode string 274 as FIG. 2I shows. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the second diode string 274.

FIG. 2J is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2J, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a diode device 208, a first diode 210 and an n-type field effect transistor 212. FIG. 2J is similar to FIG. 2A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2J further comprises a first diode string 272 as FIG. 2K shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272.

FIG. 2L is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2L, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210, an n-type field effect transistor 212, and an additional diode 282. FIG. 2L is similar to FIG. 2A except that the electrostatic discharge protection circuit 200 of the FIG. 2L further includes the additional diode 282, and the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280. The additional diode 282 has an anode coupled to the rail V_(SS) and a cathode coupled to the input/output terminal 280. The additional diode 282 is arranged to provide a discharge path to discharge the electrostatic discharge current from the rail V_(SS) to the input/output terminal 280. The input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2L further comprises a first diode string 272 and a second diode string 274 as FIG. 2M shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 2N is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2N, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210 and an n-type field effect transistor 212. FIG. 2N is similar to FIG. 2A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280. The input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2N further comprises a first diode string 272 and a second diode string 274 as FIG. 2O shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272 and the second diode string 274. In yet another embodiment, the n-type field effect transistor 212 of the electrostatic discharge protection circuit 200 of FIG. 2N further has a buck terminal coupled to the rail V_(SS) as FIG. 2P shows. Therefore, a parasitic diode 213 is formed between the input/output terminal 280 and the rail V_(SS) when the buck terminal of the n-type field effect transistor 212 is coupled to the rail V_(SS).

FIG. 2Q is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2Q, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208 and an n-type field effect transistor 212. FIG. 2Q is similar to FIG. 2A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280. The input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2Q further comprises a second diode string 274 as FIG. 2R shows. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the second diode string 274.

FIG. 2S is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2S, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a diode device 208, a first diode 210 and an n-type field effect transistor 212. FIG. 2S is similar to FIG. 2A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280. The input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2S further comprises a first diode string 272 as FIG. 2T shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272.

FIG. 2U is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 2A. As shown in FIG. 2U, the electrostatic discharge protection circuit 200 includes a first resistor 202, a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210, an n-type field effect transistor 212, and an additional diode 284. FIG. 2U is similar to FIG. 2A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280 and the electrostatic discharge protection circuit 200 of FIG. 2U further includes the additional diode 284. The input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 200. The additional diode 284 has an anode coupled to the input/output terminal 280 and a cathode coupled to the rail V_(DD). The additional diode 284 is arranged to provide a discharge path to discharge the electrostatic discharge current from the input/output terminal 280 to the rail V_(DD). In another embodiment, the electrostatic discharge protection circuit 200 of FIG. 2U further comprises a first diode string 272 and a second diode string 274 as FIG. 2V shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 2D for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 5A is a simulation diagram of leakage current in the embodiment. As the FIG. 5A shows, when the voltage at the rail V_(DD) is 1V and the pulse rise time is 1 ms, the total leakage 510 of the electrostatic discharge protection circuit 200 is 62 nA, wherein the drain leakage 512 of the n-type field effect transistor 212 is 33 nA and the drain leakage 514 of the p-type field effect transistor 204 is 28 nA. FIG. 5B is a simulation diagram of leakage current in the conventional electrostatic discharge protection circuit 100, wherein when the voltage at the rail V_(DD) is 1V and the pulse rise time is 1 ms, the total leakage 520 of the electrostatic discharge protection circuit 100 is 145 nA, and the drain leakage 524 of the p-type field effect transistor 104 is 140 nA.

Based on the FIGS. 5A and 5B, it can be known that, in the same situation, the total leakage 510 of the electrostatic discharge protection circuit 200 of the invention has a 2.5 times drastic reduction of leakage current, when compared to the total leakage 520 of the conventional electrostatic discharge protection circuit 100.

FIG. 6A is a simulation diagram of the trigger current in the embodiment. As the FIG. 6A shows, when the voltage at the rail V_(DD) is 5V and the pulse rise time is 10 ns, the trigger current I-trigger1 of the electrostatic discharge protection circuit 200 can reach 37 mA at 7 ns and 73 mA at 10 ns. FIG. 6B is a simulation diagram of the trigger current in the conventional electrostatic discharge protection circuit 100, wherein when the voltage at the rail V_(DD) is 5V and the pulse rise time is 10 ns, the trigger current 610 of the electrostatic discharge protection circuit 100 can reach 37 mA until 10 ns.

Based on the FIGS. 6A and 6B, it can be known that, in the same situation, the trigger current I-trigger1 of electrostatic discharge protection circuit 200 of the embodiment has a significant 2 times increase of the trigger current and a 33 percent forward of the trigger speed, when compared to those of the trigger current 610 of the conventional electrostatic discharge protection circuit 100.

FIG. 3A is a schematic view showing another embodiment. As shown of the FIG. 3A, the electrostatic discharge protection circuit 300 includes the first resistor 202, a third diode 303, the p-type field effect transistor 204, the second diode 206, the diode device 208, the first diode 210 and the n-type field effect transistor 212. The electrostatic discharge protection circuit 300 is similar to the electrostatic discharge protection circuit 200 in FIG. 2A. The difference is that the electrostatic discharge protection circuit 300 further includes the third diode 303. The third diode 303 has a cathode coupled to the first node N1 and an anode coupled to the third node N3. Furthermore, the third diode 303 is arranged to draw the trigger current I-trigger2 to the third node N3. For simplification, the circuit connection of the electrostatic discharge protection circuit 300 will not be described in detail here. Reference may be made to the description of FIG. 2A.

It should be noted that the diode device 208 serves as a capacitance device and is arranged to construct an RC circuit with the first resistor 202. In some embodiments, the diode device 208 has a first terminal coupled to the second node N2 and a second terminal coupled to the first node N1, and the diode device 208 can be replaced by other capacitance components, such as plate capacitors, MOS capacitors or the same. Compared with the other capacitance component, the diode device 208 can reduce the area of the electrostatic discharge protection circuit 300. In addition, the electrostatic discharge protection circuit 300 further comprises a parasitic silicon controlled rectifier 214 which comprises the p-type field effect transistor 204 and the n-type field effect transistor 212. The parasitic silicon controlled rectifier 214 has a control terminal coupled to the second node N2 and another controller terminal coupled to the third node N3. The control terminals can trigger the parasitic silicon controlled rectifier 214 by the trigger current I-trigger1 and I-trigger2. When an electrostatic discharge event occurs, the parasitic silicon controlled rectifier 214 provides a discharge path to protect the chip. In another embodiment, the electrostatic discharge protection circuit 300 can further be coupled to the discharge devices 290 and 291 (e.g., clamp device or other silicon controlled rectifier device) between the rail V_(DD) and V_(SS). During an electrostatic discharge event, the discharge devices 290 and 291 can be respectively triggered by the second node N2 and the third node N3 of the electrostatic discharge protection circuit 300 respectively to provide discharge paths to the chip. Furthermore, the discharge device 290 can be simultaneously triggered by the second node N2 and third node N3 of the electrostatic discharge protection circuit 300. Namely, the second node N2 and the third node N3 are coupled to the same discharge device 290, as shown in FIG. 3E. Note that, the electrostatic discharge protection circuit 300 can be regarded as a detecting circuit after coupled to the discharge devices 290 and/or 291.

FIG. 3B is the layout of the electrostatic discharge protection circuit 300. The electrostatic discharge protection circuit 300 includes the substrate 216, the first resistor 202, the first diode 210, the second diode 206 and the diode device 208. The diode device 208 can be replaced by the other capacitance components, such as plate capacitors, MOS capacitors or the same. The electrostatic discharge protection circuit 300 is similar to the electrostatic discharge protection circuit 200 in FIG. 2B. It should be noted that the n-type and the p-type doped regions can be served as a plurality of contact points. For example, in this embodiment, the p-type doped region 252 can be served as a first contact point, the n-type doped region 248 can be served as a second contact point, the n-type doped region 246 can be served as a third contact point, the p-type doped region 250 can be served as a fourth contact point, and the n-type doped region 368 can be served as a fifth contact point. The difference is that the electrostatic discharge protection circuit 300 further includes the third diode 303. Moreover, the substrate 216 further includes the fifth contact point (that is, the n-type doped region 368), the n-type doped region 368 and the shallow trench isolation 370. The third diode 303 has a cathode coupled to the first node N1 and an anode coupled to the fifth contact point (that is, the n-type doped region 368). The fifth contact point (that is, the n-type doped region 368) is disposed between the p-type doped region 226 and the n-type doped region 230, and used to couple the N-well 218 to the anode of third diode 303. For simplification, the circuit connection of the electrostatic discharge protection circuit 300 will not be described in detail here. Reference may be made to the description of FIG. 2B. It should be noted that the substrate 216 can be a p-type semiconductor substrate or a p-type semiconductor substrate having a P-well, wherein the n-type field effect transistor 212 is formed in the P-well. In another embodiment, the diode device 208 can be the common capacitor device and coupled between the second terminal of the first resistor 202 and the rail V_(SS). Furthermore, the N-well 218 of the electrostatic discharge protection circuit 300 can also be laterally extended to be under the fourth contact point (that is, under the p-type doped region 250), as FIG. 3C shows. In another embodiment, the electrostatic discharge protection circuit 300 can even be laterally extended to be under the fifth contact point (that is, under the n-type doped region 368), as FIG. 3D shows.

When an electrostatic discharge event occurs, similar with the electrostatic discharge protection circuit 200 of FIGS. 2A and 2B, the electrostatic discharge protection circuit 300 of FIGS. 3A and 3B discharges the electrostatic from the rail V_(DD) to the rail V_(SS) to protect the chip. Similar with the discharge paths of the electrostatic discharge protection circuit 200, the discharge paths of the electrostatic discharge protection circuit 300 is provided via the parasitic silicon controlled rectifier 214. The operations of the electrostatic discharge protection circuit 300 are similar to 200, which are not described in detail here. The difference between the electrostatic discharge protection circuits 300 and 200 is that the electrostatic discharge protection circuit 300 further includes a trigger mechanism by drawing a current.

During an electrostatic discharge event, the n-type field effect transistor 212 and the second diode 206 are conducted, such that the third diode 303 is turned on to produce a trigger current I-trigger2 since the first node N1 is under a low voltage level. The parasitic silicon controlled rectifier 214 can be triggered by injecting the trigger current I-trigger1 at the fourth contact point (i.e., the p-type doped region 250) and/or drawing the trigger current I-trigger2 of the third diode 303 from the fifth contact point (i.e., the n-type doped region 368).

In another embodiment, the electrostatic discharge protection circuit 300 of FIGS. 3A and 3B further comprises a first diode string 272 and a second diode string 274 as FIG. 3E shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. As described above, the second diode string 274 is coupled with the second diode 206 in series. The voltage difference between the gate (that is, the second gate 228) and the drain (that is, the n-type doped region 232) of the n-type field effect transistor 212 can be decreased by tuning the diode number of the second diode string 274 to reduce the leakage of the n-type field effect transistor 212. In a similar way, the first diode string 272 and the first diode 210 are coupled in series, and the leakage of the p-type field effect transistor 204 can be reduced as the voltage difference between the gate (that is, the first gate 224) and the drain (that is, the p-type doped region 222) of the p-type field effect transistor 204 is reduced by tuning the diode number of the first diode string 272.

3F is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 3A. As shown in FIG. 3F, the electrostatic discharge protection circuit 300 includes the first resistor 202, a third diode 303, the p-type field effect transistor 204, the second diode 206, the diode device 208, the first diode 210 and the n-type field effect transistor 212. FIG. 3F is similar to FIG. 3A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 300. In another embodiment, the electrostatic discharge protection circuit 300 of FIG. 3F further comprises a first diode string 272 and a second diode string 274 as FIG. 3G shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 3E for the detailed descriptions of the first diode string 272 and the second diode string 274.

3H is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 3A. As shown in FIG. 3H, the electrostatic discharge protection circuit 300 includes the first resistor 202, a third diode 303, the p-type field effect transistor 204, the second diode 206, the diode device 208, the first diode 210 and the n-type field effect transistor 212. FIG. 3H is similar to FIG. 3A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 300. In another embodiment, the electrostatic discharge protection circuit 300 of FIG. 3H further comprises a first diode string 272 and a second diode string 274 as FIG. 3I shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 3E for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 4A is a schematic view showing an embodiment disclosed by this disclosure. As shown of the FIG. 4A, the electrostatic discharge protection circuit 400 includes the first resistor 202, a second resistor 405, the p-type field effect transistor 204, the first diode 210, the second diode 206, the third diode 303, the diode device 208 and the n-type field effect transistor 212. The electrostatic discharge protection circuit 400 of this embodiment is similar to the electrostatic discharge protection circuit 300 in FIG. 3A. The difference is that the electrostatic discharge protection circuit 400 further includes the second resistor 405. The second resistor 405 has a first terminal coupled to the rail V_(SS) and a second terminal coupled to the second node N2. For simplification, the circuit connection of the electrostatic discharge protection circuit 400 will not be described in detail here. Reference may be made to the description of FIG. 3A. It should be noted that the diode device 208 serves as a capacitance device and is arranged to construct an RC circuit with the first resistor 202. In some embodiments, the diode device 208 has a first terminal coupled to the second node N2 and a second terminal coupled to the first node N1, and the diode device 208 can be replaced by other capacitance components, such as plate capacitors, MOS capacitors or the same. Compared with the other capacitance components, the diode device 208 can reduce the area of the electrostatic discharge protection circuit 400. In addition, the electrostatic discharge protection circuit 400 further comprises a parasitic silicon controlled rectifier 214 which comprises the p-type field effect transistor 204 and the n-type field effect transistor 212. The parasitic silicon controlled rectifier 214 has a terminal coupled to the anode of third diode 303, such that the parasitic silicon controlled rectifier 214 can be triggered by the trigger current I-trigger2. When an electrostatic discharge event occurs, the parasitic silicon controlled rectifier 214 provides a discharge path to protect the chip. In another embodiment, the electrostatic discharge protection circuit 400 can further be coupled to the discharge device 290 (e.g., clamp device or other silicon controlled rectifier device) between the rail V_(DD) and V_(SS). When an electrostatic discharge event occurs, the discharge device 290 can be triggered by the third node N3 of the electrostatic discharge protection circuit 400. The discharge device 290 provides a discharge path to the chip. Note that, the electrostatic discharge protection circuit 400 can be regarded as a detection circuit after being coupled to the discharge device 290.

FIG. 4B is the layout of the electrostatic discharge protection circuit 400 of FIG. 4A. The electrostatic discharge protection circuit 400 includes the substrate 216, the first resistor 202, the second resistor 405, the first diode 210, the second diode 206, the third diode 303 and the diode device 208. The diode device 208 can be replaced by the other capacitance components, such as plate capacitors, MOS capacitors or the same. The electrostatic discharge protection circuit 400 is similar to the electrostatic discharge protection circuit 300 in FIG. 3B. The difference is that the electrostatic discharge protection circuit 400 further includes the second resistor 405 coupled between the second node N2 and the rail V_(SS), and the fourth contact point (that is, the p-type doped region 250) is removed, the p-type doped region 250 is removed and the shallow trench isolations 260 of the electrostatic discharge protection circuit 300 in the substrate 216 are removed. For simplification, the circuit connection of the electrostatic discharge protection circuit 400 will not be described in detail here. Reference may be made to the description of FIG. 3B. It should be noted that the substrate 216 can be a p-type semiconductor substrate or a p-type semiconductor substrate having a P-well, wherein the n-type field effect transistor 212 is formed in the P-well. In another embodiment, the diode device 208 can be the common capacitor device and coupled between the second terminal of the first resistor 202 and the rail V_(SS). Furthermore, the N-well 218 of the electrostatic discharge protection circuit 400 can also be laterally extended to be under the fifth contact point (that is, under the n-type doped region 368), as FIG. 4C shows.

When an electrostatic discharge event occurs, similar with the electrostatic discharge protection circuit 300 of FIGS. 3A and 3B, the electrostatic discharge protection circuit 400 of FIGS. 4A and 4B discharges the electrostatic from the rail V_(DD) to V_(SS) to protect the chip. During the electrostatic discharge event, the voltage level at the gate of the p-type field effect transistor 204 (i.e., the first gate 224) is lower than that at the rail V_(DD) because of the RC delay formed by the first resistor 202 and diode device 208. Therefore, the p-type field effect transistor 204 is conducted by the voltage difference between the source and gate thereof.

The conducted p-type field effect transistor 204 turns on the first diode 210 and produces a current through the second resistor 405 to the rail V_(SS). In the meantime, the voltage of the second node N2 is increased because the p-type field effect transistor 204 and the first diode 210 are conducted and the current passes through the second resistor 405. The n-type field effect transistor 212 is turned on by the voltage difference of the source (that is, the n-type doped region 230) and the gate (that is, the second gate 228). The second diode 206 is conducted after the n-type field effect transistor 212 is conducted. Since the second diode 206 is conducted, the voltage of the first node N1 is decreased, such that the current through the conducted p-type field effect transistor 204 is increased. In light of the foregoing, the p-type field effect transistor 204 and n-type field effect transistor 212 constitute a loop circuit, such that the p-type field effect transistor 204 and n-type field effect transistor 212 can be fully conducted. The drawing way of trigger current I-trigger2 is produced by the third diode 303 due to the voltage on the first node N1 being decreased. The drawing way of the trigger current I-trigger2 is discharged through the second diode 206 and the n-type field effect transistor 212 to the rail V_(SS) and produces the source of the drawing way of the trigger I-trigger2 to trigger the parasitic silicon controlled rectifier 214 by the fifth contact point (that is, n-type doped 368).

In another embodiment, the electrostatic discharge protection circuit 400 of FIGS. 4A and 4B further comprises a first diode string 272 and a second diode string 274 as FIG. 4D shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. As described above, the second diode string 274 is coupled with the second diode 206 in series. The voltage difference between the gate (that is, the second gate 228) and the drain (that is, the n-type doped region 232) of the n-type field effect transistor 212 can be decreased by tuning the diode number of the second diode string 274 to reduce the leakage of the n-type field effect transistor 212. In a similar way, the first diode string 272 and the first diode 210 are coupled in series, and the leakage of the p-type field effect transistor 204 can be reduce as the voltage difference between the gate (that is, the first gate 224) and the drain (that is, the p-type doped region 222) of the p-type field effect transistor 204 is reduced by tuning the diode number of the first diode string 272.

FIG. 4E is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 4A. As shown in FIG. 4E, the electrostatic discharge protection circuit 400 includes the first resistor 202, a second resistor 405, the p-type field effect transistor 204, the first diode 210, the second diode 206, the third diode 303, the diode device 208 and the n-type field effect transistor 212. FIG. 4E is similar to FIG. 4A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 400. In another embodiment, the electrostatic discharge protection circuit 400 of FIG. 4E further comprises a first diode string 272 and a second diode string 274 as FIG. 4F shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 4D for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 4G is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 4A. As shown in FIG. 4G, the electrostatic discharge protection circuit 400 includes the first resistor 202, a second resistor 405, the p-type field effect transistor 204, the first diode 210, the second diode 206, the third diode 303, the diode device 208 and the n-type field effect transistor 212. FIG. 4G is similar to FIG. 4A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 400. In another embodiment, the electrostatic discharge protection circuit 400 of FIG. 4G further comprises a first diode string 272 and a second diode string 274 as FIG. 4H shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 4D for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 7A is a schematic view showing another embodiment of the electrostatic discharge protection circuit. As shown in FIG. 7A, the electrostatic discharge protection circuit 700 includes a p-type field effect transistor 204, a second diode 206, a diode device 208, a first diode 210 and an n-type field effect transistor 212. FIG. 7A is similar to FIG. 3A except that the electrostatic discharge protection circuit 700 does not include the first resistor 202 and the third diode 303, and the trigger current I-trigger2 is drawn to the first node N1. It should be noted that reference may be made to the electrostatic discharge protection circuit 300 of FIG. 3A for the detailed descriptions of the electrostatic discharge protection circuit 700.

In another embodiment, the electrostatic discharge protection circuit 700 of FIG. 7A further comprises a first diode string 272 and a second diode string 274 as FIG. 7B shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. As described above, the second diode string 274 is coupled with the second diode 206 in series. The voltage difference between the gate (that is, the second gate 228) and the drain (that is, the n-type doped region 232) of the n-type field effect transistor 212 can be decreased by tuning the diode number of the second diode string 274 to reduce the leakage of the n-type field effect transistor 212. In a similar way, the first diode string 272 and the first diode 210 are coupled in series, and the leakage of the p-type field effect transistor 204 can be reduced as the voltage difference between the gate (that is, the first gate 224) and the drain (that is, the p-type doped region 222) of the p-type field effect transistor 204 is reduced by tuning the diode number of the first diode string 272.

FIG. 7C is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 7A. As shown in FIG. 7C, the electrostatic discharge protection circuit 700 includes the p-type field effect transistor 204, the second diode 206, the diode device 208, the first diode 210 and the n-type field effect transistor 212. FIG. 7C is similar to FIG. 7A except that the source of the p-type field effect transistor 204 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 700. In another embodiment, the electrostatic discharge protection circuit 700 of FIG. 7C further comprises a first diode string 272 and a second diode string 274 as FIG. 7D shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 7B for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 7E is a schematic view showing another embodiment of the electrostatic discharge protection circuit of FIG. 7A. As shown in FIG. 7E, the electrostatic discharge protection circuit 700 includes the p-type field effect transistor 204, the second diode 206, the diode device 208, the first diode 210 and the n-type field effect transistor 212. FIG. 7E is similar to FIG. 7A except that the source of the n-type field effect transistor 212 is coupled to an input/output terminal 280, wherein the input/output terminal 280 is arranged to be coupled to a device of an internal circuit which will be protected by the electrostatic discharge protection circuit 700. In another embodiment, the electrostatic discharge protection circuit 700 of FIG. 7E further comprises a first diode string 272 and a second diode string 274 as FIG. 7F shows. The first diode string 272 at least includes a diode having an anode coupled to the cathode of the first diode 210 and a cathode coupled to the second node N2. The second diode string 274 at least includes a diode having an anode coupled to the cathode of the second diode 206 and a cathode coupled to the drain of the n-type field effect transistor 212. It should be noted that reference may be made to FIG. 7B for the detailed descriptions of the first diode string 272 and the second diode string 274.

FIG. 7G is the layout of the electrostatic discharge protection circuit 700. As shown in FIG. 7G, the electrostatic discharge protection circuit 700 includes a substrate 216. The substrate 216 includes an N-well 218, an N-well 708, an N-well 714, at least one N-well 220, a diode device 208, a p-type field effect transistor 204, an n-type field effect transistor 212, a parasitic resistor 268, a parasitic resistor 266, a first diode 210, a second diode 206, and a parasitic diode 722. The parasitic diode 722 is arranged to provide a discharge path to discharge the electrostatic discharge current from the rail V_(SS) to the rail V_(DD). It should be noted that the n-type and the p-type doped regions can be served as a plurality of contact points. For example, in this embodiment, the p-type doped region 252′ can be served as a first contact point, the p-type doped region 702 can be served as a third contact point, the p-type doped region 250 can be served as a second contact point, the n-type doped region 248′ can be served as a fifth contact point, the n-type doped region 246 can be served as a fourth contact point, and the p-type doped region 724 can be served as a sixth contact point.

The N-well 218 is formed in the substrate 216 and has a p-type doped region 702 which is arranged to serve as the third contact point and be coupled to a rail V_(DD). The N-wells 708 and 714 are also formed in the substrate 216. The substrate 216 further has a plurality of contact points, such as the n-type doped region 248′, the p-type doped region 250, the p-type doped region 252′, the p-type doped region 724, and the n-type doped region 720. It should be noted that the substrate 216 can be a p-type semiconductor substrate or a p-type semiconductor substrate having a P-well, wherein the n-type field effect transistor 212 is formed in the P-well.

An n-type doped region 704 and an n-type doped region 706 forms a parasitic resistor 268 in the N-well 218. The n-type doped region 704 is formed on the N-well 218 and coupled to the rail V_(DD). The n-type doped region 706 is formed on the N-well 218 and coupled to a first node N1. A p-type doped region 250 and the p-type doped region 252′ forms a parasitic resistor 266 in the substrate 216. The p-type doped region 250 and the p-type doped region 252′ serve as connect points, and the p-type doped region 250 is formed on the substrate 216 and coupled to a second node N2, and the p-type doped region 252′ is formed on the substrate 216 and coupled to the rail V_(SS).

The p-type field effect transistor 204 is formed on the N-well 218 and coupled to the second node N2 through the first diode 210, wherein the p-type field effect transistor 204 comprises the p-type doped region 222, the first gate 224 and the p-type doped region 226. The p-type doped region 222 is the drain of the p-type field effect transistor 204 and is formed in the N-well region 218 and coupled to the second node N2 through the first diode 210. The first gate 224 is the gate of the p-type field effect transistor 204, and coupled to the first node N1. The p-type doped region 226 is the source of the p-type field effect transistor 204, formed in the N-well 218, and coupled to the rail V_(DD).

The second diode 206 is formed on the N-well 714 and coupled between the n-type field effect transistor 212 and the first node N1, wherein the second diode 206 comprises an n-type doped region 716 and a p-type doped region 718. The n-type doped region 716 is formed on the N-well 714 and coupled to the n-type doped region 232 which is the drain of the n-type field effect transistor 212. The p-type doped region 718 is formed on the N-well 714 and coupled to the first node N1.

The diode device 208 is a capacitance diode constructed via the N-well 220 and the substrate 216, wherein the diode device 208 has a first terminal coupled to the rail V_(SS) or the second node N2 and a second terminal coupled to the first node N1 via the n-type doped region 246, wherein the first terminal of the diode device 208 is coupled to the rail V_(SS) through the p-type doped region 252′ or the p-type doped region 724.

The first diode 210 is formed on the N-well 708 and coupled between the p-type field effect transistor 204 and the second node N2, wherein the first diode 210 comprises an n-type doped region 710 and a p-type doped region 712. The n-type doped region 710 is formed on the N-well 708 and coupled to the second node N2. The p-type doped region 712 is formed on the N-well 708 and coupled to the p-type doped region 222 which is the drain of the p-type field effect transistor 204.

The n-type field effect transistor 212 is formed on the substrate 216, comprising the second gate 228, the n-type doped region 230 and the n-type doped region 232. The second gate 228 is coupled to the second node N2. The n-type doped region 230 is the source of the n-type field effect transistor 212, formed on the substrate 216, and coupled to the rail V_(SS). The n-type doped region 232 is the drain of the n-type field effect transistor 212, formed on the substrate 216, and coupled to the first node N1 through the second diode 206.

The parasitic diode 722 is formed on the substrate 216 via the p-type doped region 252′ and an n-type doped region 248′, wherein the p-type doped region 252′ and n-type doped region 248′ can serve as the first and fifth contact points, respectively. The n-type doped region 248′ is formed on the substrate 216 and coupled to the rail V_(DD). The p-type doped region 252′ is formed on the substrate 216 and coupled to the rail V_(SS).

The electrostatic discharge protection circuit 700 further includes a first parasitic silicon controlled rectifier 214 a and a second parasitic silicon controlled rectifier 214 b. The first parasitic silicon controlled rectifier 214 a comprises the p-type doped region 226 of the p-type field effect transistor 204, the N-well 218, the substrate 216 and the n-type doped region 720, wherein the path 215 a is a path of the first parasitic silicon controlled rectifier 214 a. The second parasitic silicon controlled rectifier 214 b comprises the p-type doped region 702, the N-well 218, the substrate 216, and the n-type doped region 230 of the n-type field effect transistor 212, wherein the p-type doped region 702 can serve as the third contact point, wherein the path 215 b is a path of the second parasitic silicon controlled rectifier 214 b. Moreover, the p-type doped region 250, which is coupled to the second node N2, is arranged to be a control terminal of the first parasitic silicon controlled rectifier 214 a. The n-type doped region 706, which is coupled to the first node N1, is arranged to be a control terminal of the second parasitic silicon controlled rectifier 214 b. It should be noted that, in some of the exemplary embodiments, the p-type doped region 250 is disposed between the p-type doped region 226 and the n-type doped region 720, the p-type doped region 252′ is disposed between the n-type doped region 248′ and the p-type doped region 250, and the n-type doped region 706 is disposed between the p-type doped region 702 and the n-type doped region 230.

When an electrostatic discharge event occurs, the electrostatic discharge protection circuit 700 of FIGS. 7A and 7G discharges the electrostatic current from the rail V_(DD) to the rail V_(SS) to protect the chip. At this time, the voltage level at the gate of the p-type field effect transistor 204 (i.e., the first gate 224) is lower than that at the rail V_(DD) because of the RC delay formed by the first parasitic resistor 268 and diode device 208. Therefore, the p-type field effect transistor 204 is conducted by the voltage difference between the source and gate thereof.

The conducted p-type field effect transistor 204 turns on the first diode 210 to produce the trigger current I-trigger1, which is output to the second contact point which is the p-type doped region 250 to trigger the first parasitic silicon controlled rectifier 214 a. After the first parasitic silicon controlled rectifier 214 a is triggered, the parasitic silicon controlled rectifier 214 a discharges the electrostatic current from the rail V_(DD) to the rail V_(SS). In the meantime, the voltage of the second node N2 is increased because the p-type field effect transistor 204 and the first diode 210 are turned on, and the n-type field effect transistor 212 is turned on by the voltage difference of the source (that is, the first n-type doped region 230) and the gate (that is, the second gate 228). The conducted n-type field effect transistor 212 turns on the second diode 206, such that the trigger current I-trigger2 is drawn from the n-type doped region 706 to the first node N1 in order to trigger the second parasitic silicon controlled rectifier 214 b. Furthermore, since the second diode 206 is turned on, the voltage of the first node N1 is decreased, such that the current on the conducted p-type field effect transistor 204 is increased. In light of the foregoing, the p-type field effect transistor 204 and n-type field effect transistor 212 constitute a loop, such that the p-type field effect transistor 204 and n-type field effect transistor 212 are fully conducted (i.e., turned on) and provide the trigger current to the silicon controlled rectifier 214 a and the silicon controlled rectifier 214 b continuously. It should be noted that, in another embodiment, the electrostatic discharge protection circuit 700 can also have a plurality of shallow trench isolation disposed between the doped regions to isolate the doped regions.

While the disclosure has been described by way of example and in terms of the preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

What is claimed is:
 1. An electrostatic discharge protection circuit, comprising: a p-type field effect transistor, having a source coupled to an input/output terminal, a gate coupled to a first node and a drain coupled to a second node; a capacitance device, having a first terminal coupled to a first rail and a second terminal coupled to the first node; an n-type field effect transistor, having a source coupled to the first rail, a gate coupled to the second node and a drain coupled to the first node, wherein the p-type field effect transistor is formed on a first N-well, and the first N-well and the n-type field effect transistor are formed on a substrate; a parasitic silicon controlled rectifier, wherein the parasitic silicon controlled rectifier is constructed by the source of the p-type field effect transistor, the first N-well, the substrate and the source of the n-type field effect transistor, and the parasitic silicon controlled rectifier further comprises a first control terminal coupled to the second node and/or a second control terminal coupled to the first node, wherein the parasitic silicon controlled rectifier is triggered by injecting current into the first control terminal and/or drawing current from the second control terminal.
 2. The electrostatic discharge protection circuit as claimed in claim 1, further comprising a first resistor, having a first terminal coupled to a second rail and a second terminal coupled to the first node.
 3. The electrostatic discharge protection circuit as claimed in claim 1, further comprising: a first diode, having an anode coupled to the drain of the p-type field effect transistor and a cathode coupled to the second node; and/or a second diode, having an anode coupled to the first node and a cathode coupled to the drain of the n-type field effect transistor.
 4. The electrostatic discharge protection circuit as claimed in claim 1, further comprises an additional diode having an anode coupled to the first rail and a cathode coupled to the input/output terminal.
 5. The electrostatic discharge protection circuit as claimed in claim 1, wherein a parasitic diode formed between the input/output terminal and the second rail when a buck terminal of the p-type field effect transistor is coupled to the second rail.
 6. The electrostatic discharge protection circuit as claimed in claim 1, further comprising a discharge device, having a first control terminal coupled to the second node and/or a second control terminal coupled to the first node, wherein the first control terminal and the second control terminal are arranged to trigger the discharge device.
 7. The electrostatic discharge protection circuit as claimed in claim 1, further comprising a third diode, having an anode coupled to a parasitic silicon controlled rectifier or a control terminal of a discharge device and a cathode coupled to the first node.
 8. The electrostatic discharge protection circuit as claimed in claim 7, further comprising a second resistor, having a first terminal coupled to the first rail and a second terminal coupled to the second node.
 9. The electrostatic discharge protection circuit as claimed in claim 3, further comprising: a first diode string, having an anode coupled to the cathode of the first diode and a cathode coupled to the second node; and/or a second diode string, having an anode coupled to the cathode of the second diode and a cathode coupled to the drain of the n-type field effect transistor.
 10. The electrostatic discharge protection circuit as claimed in claim 1, wherein the capacitance device is a diode device, a plate capacitor or a MOS capacitor.
 11. An electrostatic discharge protection circuit, comprising: a p-type field effect transistor, having a source coupled to a first rail, a gate coupled to a first node and a drain coupled to a second node; a capacitance device, having a first terminal coupled to a second rail and a second terminal coupled to the first node; an n-type field effect transistor, having a source coupled to an input/output terminal, a gate coupled to the second node and a drain coupled to the first node, wherein the p-type field effect transistor is formed on a first N-well, and the first N-well and the n-type field effect transistor are formed on a substrate; and a parasitic silicon controlled rectifier, wherein the parasitic silicon controlled rectifier is constructed by the source of the p-type field effect transistor, the first N-well, the substrate and the source of the n-type field effect transistor, and the parasitic silicon controlled rectifier further comprises a first control terminal coupled to the second node and/or a second control terminal coupled to the first node, wherein the parasitic silicon controlled rectifier is triggered by injecting current into the first control terminal and/or drawing current from the second control terminal.
 12. The electrostatic discharge protection circuit as claimed in claim 11, further comprising a first resistor, having a first terminal coupled to the first rail and a second terminal coupled to the first node.
 13. The electrostatic discharge protection circuit as claimed in claim 11, further comprising: a first diode, having an anode coupled to the drain of the p-type field effect transistor and a cathode coupled to the second node; and/or a second diode, having an anode coupled to the first node and a cathode coupled to the drain of the n-type field effect transistor.
 14. The electrostatic discharge protection circuit as claimed in claim 11, further comprises an additional diode having an anode coupled to the input/output terminal and a cathode coupled to the first rail.
 15. The electrostatic discharge protection circuit as claimed in claim 11, wherein a parasitic diode formed between the input/output terminal and the second rail when a buck terminal of the n-type field effect transistor is coupled to the second rail.
 16. The electrostatic discharge protection circuit as claimed in claim 11, further comprising a discharge device, having a first control terminal coupled to the second node and/or a second control terminal coupled to the first node, wherein the first control terminal and the second control terminal are arranged to trigger the discharge device.
 17. The electrostatic discharge protection circuit as claimed in claim 11, further comprising a third diode, having an anode coupled to a parasitic silicon controlled rectifier or a control terminal of a discharge device and a cathode coupled to the first node.
 18. The electrostatic discharge protection circuit as claimed in claim 17, further comprising a second resistor, having a first terminal coupled to the second rail and a second terminal coupled to the second node.
 19. The electrostatic discharge protection circuit as claimed in claim 13, further comprising: a first diode string, having an anode coupled to the cathode of the first diode and a cathode coupled to the second node; and/or a second diode string, having an anode coupled to the cathode of the second diode and a cathode coupled to the drain of the n-type field effect transistor.
 20. The electrostatic discharge protection circuit as claimed in claim 11, wherein the capacitance device is a diode device, a plate capacitor or a MOS capacitor.
 21. An electrostatic discharge protection circuit, comprising: a p-type field effect transistor, having a source coupled to a first rail, a gate coupled to a first node and a drain coupled to a second node; a capacitance device, having a first terminal coupled to a second rail and a second terminal coupled to the first node; an n-type field effect transistor, having a source coupled to the second rail, a gate coupled to the second node and a drain coupled to the first node, wherein the p-type field effect transistor is formed on a first N-well, and the first N-well and the n-type field effect transistor are formed on a substrate; a parasitic silicon controlled rectifier, wherein the parasitic silicon controlled rectifier is constructed by the source of the p-type field effect transistor, the first N-well, the substrate and the source of the n-type field effect transistor, and the parasitic silicon controlled rectifier further comprises a first control terminal coupled to the second node and a second control terminal coupled to the first node, wherein the parasitic silicon controlled rectifier is triggered by injecting current into the first control terminal and drawing current from the second control terminal.
 22. The electrostatic discharge protection circuit as claimed in claim 21, further comprising: a first diode, having an anode coupled to the drain of the p-type field effect transistor and a cathode coupled to the second node; and/or a second diode, having an anode coupled to the first node and a cathode coupled to the drain of the n-type field effect transistor.
 23. The electrostatic discharge protection circuit as claimed in claim 21, further comprising a discharge device, having a first control terminal coupled to the second node and/or a second control terminal coupled to the first node, wherein the first control terminal and the second control terminal are arranged to trigger the discharge device.
 24. The electrostatic discharge protection circuit as claimed in claim 21, wherein the capacitance device is a diode device, a plate capacitor or a MOS capacitor.
 25. The electrostatic discharge protection circuit as claimed in claim 22, further comprising: a first diode string, having an anode coupled to the cathode of the first diode and a cathode coupled to the second node; and/or a second diode string, having an anode coupled to the cathode of the second diode and a cathode coupled to the drain of the n-type field effect transistor.
 26. An electrostatic discharge protection circuit, comprising: a substrate, having a first contact point, a second contact point and a first n-type doped region; a first N-well, formed in the substrate, having a third contact point coupled to a first rail; a second n-type doped region, formed on the first N-well and coupled to the first rail; and a third n-type doped region, formed on the first N-well and coupled to a first node; a p-type field effect transistor, formed on the first N-well, comprising: a first p-type doped region, formed on the first N-well and coupled to a second node; a first gate, coupled to the first node; and a second p-type doped region, formed on the first N-well and coupled to the first rail; an n-type field effect transistor, formed on the substrate, comprising: a second gate, coupled to the second node; a fourth n-type doped region, formed on the substrate and coupled to a second rail; and a fifth n-type doped region, formed on the substrate and coupled to the first node; a capacitance device, having a first terminal coupled to the second rail and a second terminal coupled to the first node, wherein the second contact point is coupled to the second node, and the first contact point and the first n-type doped region are coupled to the second rail; a first parasitic silicon controlled rectifier, wherein the first parasitic silicon controlled rectifier comprises the second p-type doped region of the p-type field effect transistor, the first N-well, the substrate and the first n-type doped region, wherein a first parasitic resistor is formed on the substrate by the second contact point and the first contact point; a second parasitic silicon controlled rectifier, wherein the second parasitic silicon controlled rectifier comprises the third contact point, the first N-well, the substrate and the fourth n-type doped region of the n-type field effect transistor, wherein the third contact point is a fifth p-type doped region, wherein a second parasitic resistor is formed on the first N-well by the second n-type doped region and the third n-type doped region.
 27. The electrostatic discharge protection circuit as claimed in claim 26, further comprising: a second N-well, formed in the substrate; a first diode, formed on the second N-well, comprising: a sixth n-type doped region, formed on the second N-well and coupled to the second node; and a third p-type doped region, formed on the second N-well and coupled to the first p-type doped region; a third N-well, formed in the substrate; and a second diode, formed on the third N-well, comprising: a seventh n-type doped region, formed on the third N-well and coupled to the fifth n-type doped region; and a fourth p-type doped region, formed on the third N-well and coupled to the first node.
 28. The electrostatic discharge protection circuit as claimed in claim 26, wherein the second contact point is disposed between the second p-type doped region and the first n-type doped region, the third n-type doped region is disposed between the third contact point and the fourth n-type doped region.
 29. The electrostatic discharge protection circuit as claimed in claim 28, wherein the first contact point is a sixth p-type doped region formed on the substrate, the second contact point is a seventh p-type doped region formed on the substrate, and a fourth contact point is an eighth n-type doped region formed on a fourth N-well.
 30. The electrostatic discharge protection circuit as claimed in claim 26, wherein the capacitance device is a diode device.
 31. The electrostatic discharge protection circuit as claimed in claim 30, wherein the diode device comprises at least one fourth N-well and the substrate, the fourth N-well includes the fourth contact point coupled to the first node, and the first terminal of the capacitance device is coupled to the second rail through the first contact point. 